This invention pertains generally to metal detectors and more particularly to a metal detector of the type having a tuned sensing loop transducer which undergoes a shift in resonance and Q when brought into proximity to metal objects.
In such detectors, the transducer is driven by a signal which is slightly off the resonance frequency of the transducer. As metal objects alter the resonance and Q of the transcuer, the signal developed across the transducer undergoes changes in amplitude and phase which can be detected and used to drive lamps, voltmeters, audio systems and other indicators. The changes in inductance produced by a metal object can be quite small (e.g., 0.0001%), and an extremely sensitive system is required to detect such small changes. In prior art systems, noise and changes induced by temperature and power supply variations have prevented reliable operation at such levels.